To the Editor:-Fierobe et al. [1]describe a patient in whom rhabdomyolysis associated with isoflurane anesthesia developed. They cited the Clinical Grading Scale [2]and assigned the patient a rank of 3 (total score = 18, "somewhat less than likely"). However, they failed to consider the muscle rigidity of the left arm described in their case report. This raises the rank to 4 (total score = 33, "somewhat greater than likely").

"The Clinical Grading Scale ranks the qualitative likelihood that an adverse anesthetic event represents malignant hyperthermia (MH). The assigned rank represents a lower bound on the likelihood of MH." [2]The Grading Scale is meant to provide an agreed-on clinical case definition of MH. It does not rely on data from in vitro contracture testing when used to rank a possible MH event.

The Grading Scale is of limited usefulness when data are absent. This usually occurs because laboratory tests are not performed during the event. Clinicians are urged to perform serial arterial or venous blood gas (or both), serum potassium concentrations, and creatinine kinase measurements when a possible MH episode occurs. In the case of Fierobe et al., [1]the clinical signs were present, but the authors failed to score all of them when determining the patient's probable rank.

Gregory Allen, M.D., F.R.C.P.C.

Director; North American Malignant Hyperthermia Registry; Malignant Hyperthermia Association of the United States; Sherburne, New York; Associate Professor of Anesthesia; College of Medicine; The Pennsylvania State University; Hershey, Pennsylvania

(Accepted for publication May 15, 1998.)

Fierobe I, Nivoche Y, Mantz J, Elalaoui Y, Veber B, Desmonts JM: Perioperative severe rhabdomyolysis revealing susceptibility to malignant hyperthermia. Anesthesiology 1998; 88:263-5
Larach MG, Localio AR, Allen GC, Denborough MA, Ellis FR, Gronert GA, Kaplan RF, Muldoon SM, Nelson TE, Ording H, Rosenberg H, Waud Be, Wedel DJ: A clinical grading scale to predict malignant hyperthermia susceptibility. Anesthesiology 1994; 80:771-9